1. Field of the Invention
The present invention relates to a method of producing high-density slurry/prill explosives in boreholes, and more particularly to the production of such products by bulk-loading sensitized blends of ammonium nitrate (AN) prills and water-bearing products that contain an inorganic oxidizing salt, e.g., AN, in aqueous solution. The invention also relates to certain blends which are especially adapted to be used as starting materials in the present method, and to products made by the method.
2. Description of the Prior Art
Water-bearing explosives contain an inorganic oxidizing salt, predominantly AN, in aqueous solution, and fuel and sensitizer components. In the type commonly referred to as water gels, the aqueous salt solution is a continuous phase that is thickened or gelled. In the type known as emulsion explosives, the aqueous salt solution is the discontinuous or dispersed phase of a water-in-oil emulsion, the continuous phase of the emulsion being an oil, which is a fuel component. Water-bearing explosives are delivered into boreholes in packaged form, e.g., in bags or cartridges, and in bulk form. Cartridges are dropped, pushed with a loading pole, and pneumatically delivered, while bulk products are pumped.
In recent years, explosives have been developed which comprise a blend of AN prills and a water-in-oil emulsion (see, for example, U.S. Pat. Nos. 4,111,727 (Clay), 4,181,546 (Clay), and 4,555,278 (Cescon and Millet). The blends described in U.S. Pat. No. 4,111,727, which may contain crystalline or flake AN instead of AN prills, are stated to be sort of grout-like materials, largely solid in nature. Of the 10-40% slurry content range disclosed, the 20-35% range is stated to be preferred, and the 30-40% range is described as the preferred embodiment in the working examples. Auger-type delivery means are mentioned. U.S. Pat. No. 4,181,546 describes 40/60 to 60/40 emulsion/AN blends as containing too high a proportion of dry ingredient to be pumpable in conventional slurry pumps, but says that they are deliverable to a borehole by an auger in the same manner as dry ANFO. U.S. Pat. No. 4,555,278 describes pumping blends containing up to about 50 percent prills by weight, and augering blends containing up to about 70 percent prills by weight into packages.
U.S. Pat. No. 4,294,633 (Clay) describes a blasting agent in which a non-aqueous slurry (a solution of AN in methanol or ethylene glycol) partially fills the interstices and pores in and between AN granules to form a plastic solid mass that can be augered or otherwise conveyed through a conduit.
Our co-pending U.S. application Ser. No. 710,542, filed concurrently herewith, describes storage-stable explosive compositions comprising a sensitized blend of solid particulate inorganic nitrate, preferably AN or ANFO prills, and an aqueous slurry comprising a thickened aqueous solution of an inorganic oxidizing salt, preferably AN. Of the blend compositions described in the latter co-pending application, those which contain about 75 percent or more prills by weight are stated to be essentially in the form of a granular mass of free-flowing slurry-bearing AN prills having a higher bulk density and blasting energy than AN prills alone. While this granular product doubtlessly constitutes a valuable explosive product for the blaster to have at his disposal, a granular product of higher loaded density would be of great advantage, especially if it could be produced by a rapid-loading technique. Slurry/prill explosives, including the granular free-flowing slurry-bearing prills, are hybrid products and could be unpredictable relative to their response to handling, environment, etc. Regardless of how high the prill/slurry ratio may be, the presence of the water-bearing component cannot be overlooked and is an over-riding factor in product-handling considerations. Whether the slurry component of the product happens to be a water gel or an emulsion, the physical structure of the blend, and consequently the blend's behavior under a given set of conditions, will depend greatly on the physical structure of the slurry per se and of the prills. These blend characteristics have been unpredictable owing to the fact that the solution phases present in the slurry can undergo change when the slurry is in contact with the prills.
It has been known for many years that dry ANFO prills can be loaded into boreholes pneumatically. However, slurry/prill blends in the form of free-flowing discrete particles have not heretofore been described or suggested, and until now only augering and pumping methods have been proposed for delivering prill blend products into boreholes.